JP6247942B2 - Method for producing precast concrete member - Google Patents

Description

The present invention relates to the production how the precast concrete part.

As the strength of concrete increases, heat generation and self-shrinkage associated with the hydration reaction increase.
Therefore, when a reinforcing bar is arranged on a concrete member constructed of high-strength concrete, a fine shrinkage crack may occur due to the restriction of the reinforcing bar.

For the purpose of suppressing such shrinkage cracks, there is a method of reducing the shrinkage of the concrete itself by adding a shrinkage reducing agent or an expansion material to the concrete.
However, the use of a shrinkage reducing agent or an expanding material has hindered cost reduction.

  For this reason, in Patent Document 1, a part of the main muscle that restrains the contraction of concrete is replaced with a sheath pipe having low axial rigidity to reduce the restraining force of the main muscle and to circulate the cooling medium. Has been embedded in the vicinity of the center of the cross section of the concrete member, and a method for manufacturing a precast member is disclosed in which the temperature difference between the member surface and the inside of the member when the strength of the concrete is developed is reduced.

Japanese Patent No. 4651025

  Even when the manufacturing method of the precast member described in Patent Document 1 is adopted, the shrinkage of high-strength concrete due to the adhesion between the main reinforcement (rebar) other than the main reinforcement (rebar) replaced with the sheath tube and the concrete As a result, the fine cracks around the main muscles could not be greatly reduced.

The present invention has been made to solve the above problems, to provide a manufacturing how possible with the precast concrete part to significantly reduce the fine cracks that occur during concrete strength expression Is an issue.

  In order to solve the above problems, a method for producing a precast concrete member according to the present invention includes a step of placing a sheath tube on a mold and placing concrete on the mold, and a step of primarily curing the concrete. A step of secondary curing the concrete in a state where a compressive force is introduced into the hardened body of the concrete using a tension material inserted into the sheath tube, a step of releasing the compressive force, and a reinforcing bar in the sheath tube And a step of filling with a filler.

  According to such a method for producing a precast concrete member, a dense concrete is formed by applying a compressive force (prestress) to a hardened concrete at a stage where strength development is progressing. In addition, when a reinforcing bar is embedded in concrete, the length of the reinforcing bar is also shortened by pre-stress, so that the embedded reinforcing bar can be restrained from restraining the self-shrinkage of the concrete. Therefore, even if an admixture such as an expansion material and a shrinkage reducing agent is not added, or even if the addition amount is reduced, fine cracks accompanying self-shrinkage can be greatly reduced.

  In addition, you may perform the said secondary curing by 50 degreeC or more high temperature curing. Moreover, after performing the said secondary curing at normal temperature, you may increase the said compression force and may perform a tertiary curing further by high temperature curing of 50 degreeC or more.

  Further, in the method for producing a precast concrete member, an inner mold for forming a through hole in the hardened body is disposed in the center of the mold, and the outer peripheral surface of the hardened body and the If it heats from a through-hole, it can harden | cure efficiently by heating from the outer side and the inner side of the hardening body of concrete. Therefore, it becomes possible to manufacture a dense and high-strength precast concrete member.

According to the manufacturing how the precast concrete part of the present invention, it is possible to significantly reduce or eliminate the fine cracks that occur during the strength of the concrete expression.

(A) is a cross-sectional view which shows the precast concrete member which concerns on 1st embodiment, (b) is the longitudinal cross-sectional view. (A)-(c) is a cross-sectional view and a top view which show each construction step of the manufacturing method of the precast concrete member which concerns on 1st embodiment. (A)-(c) is explanatory drawing of the determination method of the amount of reinforcing bars of the precast concrete member concerning a first embodiment. (A) And (b) is a perspective view of the precast concrete member which concerns on 2nd embodiment. It is sectional drawing which shows the usage example of a precast concrete member. (A) is a figure which shows the precast concrete member which concerns on another form, (b) is sectional drawing which shows the other usage example of the same precast concrete member.

<First embodiment>
Hereinafter, the manufacturing method of the precast concrete member 1 of 1st embodiment is demonstrated.
As shown in FIGS. 1A and 1B, the precast concrete member 1 includes a hardened concrete body 2, a plurality of main bars 3 and 4 arranged along the axial direction of the hardened body 2, and a main bar. , Which are arranged so as to surround 3, 4.

The hardened body 2 is made of so-called high-strength concrete (architecture standard specification / commentary JASS5 reinforced concrete construction: design standard strength of 36 N / mm ² or more in the Architectural Institute of Japan). In the present embodiment, an ultra-high strength fiber reinforced concrete having a design standard strength of 150 N / mm ² or more is adopted as the high strength concrete. The ultra-high-strength concrete in this specification is a concrete having a design standard strength of 100 N / mm ² or more.
In addition, the kind of high-strength concrete which comprises the hardening body 2, and design standard intensity | strength are not limited.

  High-strength concrete is composed of a mixture including at least a binder, water, fine aggregate, coarse aggregate, a water reducing agent, and fibers. The binder contains at least cement and silica fume. Further, an admixture such as blast furnace slag fine powder may be included as long as it does not adversely affect the compressive strength and fluidity.

  In addition, what is necessary is just to set the mixing | blending of high strength concrete suitably. Moreover, the fiber used for the high-strength concrete is not limited, for example, various fibers such as steel fiber, polypropylene fiber, and vinylon fiber, or those obtained by appropriately combining a plurality of fibers from these fibers. Use it.

  In this embodiment, the case where the cured body 2 is formed in a square cross section will be described. However, the cross sectional shape of the cured body 2 is not limited, and may be, for example, a circle, an ellipse, a rectangle, or other polygons. There may be.

A through hole 6 is formed in the central portion of the cross section of the cured body 2 along the axial direction.
The through hole 6 has a circular cross section. In addition, the cross-sectional shape and dimension of the through-hole 6 are not limited, and may be appropriately set within a range that does not affect the strength of the precast concrete member 1.
Moreover, what is necessary is just to form the through-hole 6 as needed, and you may abbreviate | omit. For example, in the case of a concrete member having a square cross section with a side of 300 mm or less, the temperature difference between the surface and the center portion at the time of high-temperature curing is small, so the through-hole 6 need not be formed.

As shown in FIG. 1 (a), in this embodiment, four main bars 3, 3,... Arranged at the four corners of the precast concrete member 1 and four arranged at the corners other than the corners. A total of 8 main muscles are arranged, including the main muscles 4, 4,.
The number and arrangement of the main bars 3 and 4 are not limited.

  Of the eight main bars, the main bar 3 arranged at the corner of the hardened body 2 includes a sheath pipe 7 piped along the axial direction of the hardened body 2 and a reinforcing bar 8 disposed in the sheath pipe 7. And a filler 9 filled in a gap between the sheath tube 7 and the reinforcing bar 8.

  The sheath tube 7 is piped over the entire length of the cured body 2 in the longitudinal direction. In addition, what is necessary is just to set the internal diameter of the sheath pipe | tube 7 suitably according to the reinforcement diameter of the reinforcement 8 (main reinforcement).

The reinforcing bar 8 is integrated with the sheath tube 7 via the filler 9.
Although the material which comprises the reinforcement 8 is not limited, What is necessary is just to use a deformed reinforcement and a screw reinforcement.

  Moreover, although the material which comprises the filler 9 is not limited, What is necessary is just to use cement type fillers, such as grout and a non-shrink mortar, for example.

  The main reinforcing bars 4, 4,... Arranged other than the corners are made of reinforcing bars (deformed reinforcing bars) and are directly embedded in the hardened body 2. The main bars 4, 4,... Arranged other than the corners may be constituted by the sheath tube 7, the reinforcing bars 8, and the filler 9 in the same manner as the corner main bars 3.

  The manufacturing method of a precast concrete member is provided with the preparation casting process, the primary curing process, the secondary curing process, the unloading process, and the filling process.

In the preparation placing step, as shown in FIG. 2 (a), the main bars 4, 4,... And the force distribution bars 5, 5,. Is the step of placing concrete in the mold 10 after piping.
At this time, an inner mold 11 for forming the through hole 6 is arranged in the center of the mold 10.

In the present embodiment, a sheath tube is piped as the inner mold 11.
In addition, the material which comprises the inner mold 11 is not limited, For example, the cylindrical member which consists of a vinyl chloride pipe which can be removed after curing, a paper pipe, etc., the material which melts at the time of high temperature curing, etc. are used. May be.
Moreover, the concrete placing method is not limited, and may be appropriately performed.

The primary curing process is a process in which the concrete placed on the mold 10 is primarily cured.
The primary curing is performed on the high-strength concrete placed in the mold 10 until a strength capable of demolding is developed.

  In the present embodiment, the primary curing is performed at room temperature, but the management method during the primary curing is not limited.

  The secondary curing step is a step of secondarily curing the concrete in a state where a compressive force is introduced into the hardened concrete body 2 after demolding.

When a compressive force is introduced into the cured body 2, first, the tendon 12 is inserted into the sheath tube 7.
As shown in FIG. 2B, both ends of the tendon 12 are fixed to the bearing plates 13 and 13 disposed on both end surfaces of the cured body 2. The concrete strength of the cured body 2 during tension may be 20 N / mm ² or more.
Pre-stress is less than the value obtained by multiplying the concrete strength of the hardened body 2 during tension by 0.45 (pre-stress concrete design and construction standards, same explanation: Architectural Institute of Japan) and the self-shrinkage strain in the secondary curing process. It is preferable to introduce a compressive force with which the elastic strain due to prestress is comparable.

  In the present embodiment, a screw rebar is adopted as the tension member 12, but the material constituting the tension member 12 is not limited. For example, a PC steel wire, a PC steel strand, or a PC steel rod may be used. Good.

After introducing the tensile force to the tension member 12 with the end of the tension member 12 penetrating the bearing plate 13, the tension member 12 is fixed to the bearing plate 13 by fastening the nut 14 to the end of the tension member 12. To do.
And the pre-stress acts on the hardening body 2 via the bearing plate 13 by canceling the tensile force of the tendon 12.

  The timing for inserting the tendon 12 into the sheath tube 7 is not limited. For example, it may be performed before demolding, after demolding, or simultaneously with demolding.

  In the secondary curing process of the present embodiment, the cured body 2 is cured by so-called heat curing (high temperature curing) in which the cured body 2 is heated to 50 ° C. or higher.

In this embodiment, it heats with 50 degreeC air in a high temperature curing tank.
At this time, as shown in FIG. 2C, the blower 15 is used to blow high temperature air to the through hole 6, thereby heating from the outer peripheral surface of the cured body 2 and the through hole 6.
By heating using the through-hole 6, the apparent thickness of the member that transmits heat is about half that of the conventional one, so that efficient heat curing is possible.

  In addition, in a secondary curing process, you may heat from the inside of the through-hole 6 by inserting a rod-shaped heater in the through-hole 6, and the heating method in a secondary curing process is not limited.

  By completing the heat curing in the secondary curing process, a dense and high-strength cured body 2 is completed.

The unloading step is a step of releasing the tension force of the tendon material 12 (compression force of the cured body 2).
The tension force of the tension material 12 (compression force of the cured body 2) is released by removing the nut 14 from the tension material 12.

The filling step is a step of arranging the reinforcing bar 8 in the sheath tube 7 and filling the filler 9.
As the reinforcing bar 8, the screw reinforcing bar used as the tension member 12 may be used as it is, or the tension member 12 may be extracted from the sheath tube 7 and a new reinforcing bar 8 may be inserted into the sheath tube 7.

  Along with the reinforcement of the reinforcing bar 8 to the sheath tube 7, the filler 9 is injected into the sheath tube 7 to fill the gap between the sheath tube 7 and the reinforcing bar 8.

  As mentioned above, according to the manufacturing method of the precast concrete member of this embodiment, dense concrete is formed by giving compressive force (prestress) to the hardening body 2 in the stage where intensity | strength expression is advancing. Moreover, since the length of the main reinforcement 4 is shortened by the prestress, it can suppress that the main reinforcement 4 restrains the self contraction of concrete. Therefore, even if an admixture such as an expansion material and a shrinkage reducing agent is not added, or even if the addition amount is reduced, fine cracks accompanying self-shrinkage can be greatly reduced.

  More specifically, during the curing period, self-shrinkage strain generated in the concrete and elastic strain due to compressive force (pre-stress) are generated in the hardened body 2, but the curing progresses due to the elastic strain and creep strain due to the compressive force. As a result, it apparently shifts to self-shrinkage of concrete (mutual interference), and the strain due to compressive force decreases. Further, the main bars 4, 4,... And the sheath tube 7 are shrunk while maintaining the same strain as the concrete by the compressive force. Therefore, the main reinforcement 4 and the sheath tube 7 do not constrain the shrinkage strain of the concrete, and fine cracks in the strength development process are suppressed.

  Moreover, it can cure efficiently by heating from the outer side and the inner side (the inner surface of the through-hole 6) of the concrete hardened body 2. Therefore, it becomes possible to manufacture a dense and high-strength precast concrete member.

  Further, since the reinforcing bar 8 is inserted into the sheath tube 7 after the curing period of the hardened body 2, the tension member 12 can be inserted into the sheath tube 7 during the curing period, and the tension member 12 can cure during curing. Prestress can be applied to the body 2. The hardened body 2 cured in a prestressed state has a dense structure.

  Moreover, since it becomes possible to heat the hardening body 2 from the circumference | surroundings and center (through-hole 6), the thickness which apparent heat transfers becomes about a half compared with the past. Therefore, efficient heat curing is possible.

  Assuming that the shrinkage of the concrete (self-shrinkage and creep) has completely converged upon completion of curing, if there is a residual tension, the elastic and compressive strain (recovery strain) due to the tension is applied to the concrete and the main reinforcement 4 Although it will occur, since the concrete contracts during the curing period and stress is redistributed, the burden ratio of the compressive force is significantly larger in the main reinforcement 4.

Therefore, when the residual tension is released, the compressive strain of the main bars is greatly reduced, the strain of the concrete changes from the compressive strain to the tensile strain, and depending on the amount of the main bars 4, 4,. May occur. Therefore, when the reinforcing bar (main reinforcing bar 4) is directly embedded in the concrete (hardened body 2), it is necessary to appropriately manage the amount of the reinforcing bar.
Therefore, below, the determination method of the amount of reinforcing bars is demonstrated with reference to FIG.

  In this description, as shown in FIG. 3A, one end of the precast concrete member 1 is a fixed end and the other end is a free end, and the main bars 4, 4,. Concrete removal and high temperature curing shall be performed with the adhesion removed.

  In this state, when strength develops in the concrete, as shown in FIG. 3B, the hardened body 2 shrinks due to self-shrinkage of the concrete (shrink amount L). After pushing the main bars 4, 4,... To the end surface of the cured body 2 from this state, the state where the adhesion between the main bars and the concrete is restored (see FIG. 3C) is equivalent to the state after the unloading process. It becomes.

At this time, tensile stress ( _c σ _t ) is generated in the cured body 2, and compressive stress ( _s σ _c ) acts on the main bars 4, 4,.
Tensile force of the cured body 2 (= Ac · _c σ _t , where Ac is the cross-sectional area of the cured body excluding the main muscle) and compression force of the main muscle 4 (= ΣAs · _s σ _c , where As is the total main muscle If the tensile stress _c σ _t of the concrete in this state is equal to or lower than the tensile strength of the concrete at the completion of production, the precast concrete member 1 will not be cracked.

Embedded with self-shrinking strain of concrete (unconstrained material test value), concrete material property values (Young's modulus, tensile strength), cross-sectional area of concrete part of precast concrete member 1 and Young's modulus of main reinforcement 4 as known values While changing the amount of the main reinforcing bars 4, the amount of reinforcing bars in which the tensile stress _c σ _t of the concrete does not exceed the tensile strength of the concrete is calculated by convergence calculation. In addition, what is necessary is just to use the test value by the same concrete specimen beforehand for the material characteristic value of concrete.
Thus, the appropriate amount of reinforcing bars varies depending on the material properties of the concrete. For example, the fiber reinforced concrete mixed with steel fibers has an increased tensile strength, so that the amount of the main reinforcement 4 to be embedded can be increased.

<Second Embodiment>
As shown in FIGS. 4A and 4B, the precast concrete member 1 of the second embodiment includes a hardened concrete body 2 and a plurality of main bars arranged along the axial direction of the hardened body 2. 3, a sheath tube 7 piped along the axial direction of the cured body 2, a reinforcing bar 8 disposed in the sheath tube 7, and a filler filled in a gap between the sheath tube 7 and the reinforcing bar 8. 9 is different from the precast concrete member 1 of the first embodiment.

  Since the details of the hardened body 2, the main muscle 3 and the distribution bar 5 are the same as the contents shown in the first embodiment, the detailed description is omitted.

The manufacturing method of the precast concrete member of 2nd embodiment is equipped with the preparation and placement process, the primary curing process, the secondary curing process, the tertiary curing process, the unloading process, and the filling process.
The details of the preparation / placement process, the primary curing process, the unloading process, and the filling process are the same as the contents shown in the first embodiment, and a detailed description thereof will be omitted.

The secondary curing step is a step of secondarily curing the concrete in a state where a compressive force is introduced into the hardened concrete body 2 after demolding.
In this embodiment, secondary curing is performed at room temperature. Since the details of the other secondary curing are the same as the contents shown in the first embodiment, the detailed description is omitted.

The tertiary curing process is a process of performing tertiary curing by high-temperature curing at 50 ° C. or higher after increasing the tension applied to the tendon material 12 from the end of the secondary curing process.
The tertiary curing process is performed after the secondary curing is performed at room temperature.
In this embodiment, it heats with 50 degreeC air in a high temperature curing tank.

In high temperature curing, high temperature air is blown into the through hole 6 using a blower. If it carries out like this, the hardening body 2 will be heated from the outer peripheral surface of the hardening body 2, and the inner surface of the through-hole 6. FIG.
As a result, the apparent thickness of the member to which heat is transmitted is about half that of the prior art, so that efficient heat curing is possible. In addition, the heating method of the hardening body 2 is not limited.

  When the heat curing in the tertiary curing process is completed, a dense and high-strength cured body 2 is completed.

  According to the method for producing a precast concrete member of the present embodiment, fine cracks generated in the cured body 2 can be greatly reduced or eliminated, and dense concrete can be produced. The reason is as follows.

  First, since the axial rigidity of the sheath tube 7 is extremely smaller than that of the reinforcing bar, the restraining force of the concrete by the sheath tube 7 is negligibly small. Therefore, fine cracks are unlikely to occur around the sheath tube 7.

Next, since compressive force is applied to the hardened body 2 during the curing of the concrete, the fine concrete damage caused by the creep accompanying the hydration reaction during the high temperature curing is repaired as needed, and the dense concrete It becomes.
In addition, the tension | tensile_strength force provided to the tension material 12 at the time of curing is made into the grade which the distortion more than the assumption shrinkage | contraction amount (about 500-1500 micrometers) of the concrete in an intensity | strength expression process arises.

  In this embodiment, a two-stage tension force introduction method (a relatively small tension force is introduced at the beginning of normal temperature curing, and over tension (2 at normal temperature is applied to the tension force corresponding to the concrete strength at that time). Since a method of imparting about twice the tension force) is employed, a reasonably high-quality precast concrete member 1 can be manufactured.

  When the compressive force applied to the hardened body 2 (tensile force applied to the tension material 12) is released, the elastic compressive strain (recovery creep) determined by the residual tensile force and the Young's modulus of the concrete at the completion of curing disappears. On the other hand, the self-shrinkage of concrete due to strength development during curing and the compressive strain due to creep are almost converged (non-recovery prep). Therefore, the concrete is compacted by the non-recovery creep strain, and as a result, the concrete becomes dense.

For example, in the case of high-strength concrete of Fc 200 or higher, the concrete strength may exceed 100 N / mm ² at room temperature before high-temperature curing. In that case, a larger compressive force can be introduced into the hardened body 2. After the high temperature curing, a large non-recovery strain occurs, and the concrete becomes denser.

  Since the effects of the precast concrete member manufacturing method and the precast concrete member 1 according to the other second embodiment are the same as the contents shown in the first embodiment, detailed description thereof is omitted.

  The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiments, and the above-described constituent elements can be appropriately changed without departing from the spirit of the present invention.

For example, the use of the precast concrete member 1 is not limited.
The precast concrete member 1 may be applied to a pillar as shown in FIG. In this case, the filling material 9 may be injected into the sheath tube 7 simultaneously with the injection of the joint material 16.
Further, the reinforcing bar 8 may be protruded from the end face of the hardened body 2, and this may be used as a joining bar in a joint portion with another structure (for example, the foundation 17).

  Moreover, as shown in FIG. 6, the precast concrete member 1 may be formed in a flat cross section and applied to a beam. In addition, if the edge part of the reinforcing bar 8 is made to protrude from the end surface of the hardening body 2, it can be used as another part and a joining bar.

  Further, as shown in FIG. 6B, a plurality of precast concrete members 1, 1, 1 may be connected to form a long span beam. Although the joining method of the precast concrete members 1 is not limited, For example, what is necessary is just to join by a crimping joint.

  In each of the above-described embodiments, the case where the thread reinforcement is used as the tension member and is diverted to the main reinforcement of the precast concrete member after the tension has been described, but the main reinforcement 8 is newly added after the tension member is removed from the sheath tube 7. You may arrange the bars.

  Although the case where air is supplied to the through hole formed in the center of the cross section during high temperature curing has been described, air may be supplied to the sheath tube 7 piped for the main muscle.

DESCRIPTION OF SYMBOLS 1 Precast concrete member 2 Hardened body 3 Main reinforcement 4 Main reinforcement 5 Distributing reinforcement 6 Through-hole 7 Sheath tube 8 Reinforcement 9 Filler 10 Mold 11 Inner mold 12 Tension 13 Supporting plate 14 Nut 15 Blower

Claims (4)

Placing a sheath tube on the mold and placing concrete on the mold;
A step of primarily curing the concrete;
Secondary curing of the concrete in a state where a compressive force is introduced into the hardened body of the concrete using a tendon inserted into the sheath tube;
Releasing the compression force;
A method of manufacturing a precast concrete member, comprising: arranging reinforcing bars in the sheath tube and filling a filler.   The method for producing a precast concrete member according to claim 1, wherein the secondary curing is performed at a high temperature curing of 50 ° C or higher.   2. The production of the precast concrete member according to claim 1, further comprising a step of performing tertiary curing by high temperature curing at 50 ° C. or more after increasing the compressive force after performing the secondary curing at normal temperature. Method. An inner mold for forming a through hole in the cured body is disposed in the center of the mold,
The method for producing a precast concrete member according to claim 2 or 3, wherein heating is performed from an outer peripheral surface of the cured body and the through hole during the high temperature curing.

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